Well, "unique" as in "the only time that number would be used by the company"? or as in "the only time that number would be used, ever, in the history of the nation of Japan"?

Bad enough if the ff the former: a six-digit number scheme means that the company would never be able to manufacture more than a million instruments -- 000000 through 999999. Seeing as Lyon & Healy claimed in 1892 to produce 100,000+ instruments annually, it seems unlikely a modern mass-manufacture company would tie themselves down to a mere million for all eternity.